1. Field of the Invention
The present invention relates to a method of and apparatus for upgrading heavy hydrocarbon feeds. In particular, the method and apparatus include gasification of heavy high-carbon content by-products produced by the upgrading of the heavy hydrocarbon feeds.
2. Description of the Prior Art
Many types of heavy crude oils contain high concentrations of sulfur compounds, organo-metallic compounds and heavy, non-distillable fractions called asphaltenes which are insoluble in light paraffins such as normal pentane. Because most petroleum products used for fuel must have a low sulfur content to comply with environmental regulations and restrictions, the presence of sulfur compounds in the non-distillable fractions reduces their value to petroleum refiners and increases their cost to users of such fractions as fuel or raw material for producing other products. It is desirable to remove the non-distillable fractions, or asphaltenes, from the oil because not only do the non-distillable fractions contain high amounts of sulfur, the asphaltenes tend to solidify and foul subsequent processing equipment. Removal of the asphaltenes also tends to reduce the viscosity of the oil.
Solvent extraction of asphaltenes is used to process crude and produces deasphalted oil (DAO) which is subsequently further processed into more desirable products. The deasphalting process typically involves contacting a heavy oil with a solvent. The solvent is typically an alkane such as propane, butane and pentane. The solubility of the solvent in the heavy oil decreases as the temperature increases. A temperature is selected wherein substantially all the paraffinic hydrocarbons go into solution, but where a portion of the resins and asphaltenes precipitate. Because the solubility of the asphaltenes is low in the oil-solvent mixture, the asphaltenes will precipitate out and are further separated from the DAO.
In order to increase the saleability of these hydrocarbons, refiners must resort to various expedients for removing sulfur compounds. A conventional approach for removing sulfur compounds in distillable fractions of crude oil is catalytic hydrogenation in the presence of molecular hydrogen at moderate temperature and pressure. While this approach is cost effective in removing sulfur from distillable oils, problems arise when the feed includes metal-containing asphaltenes. Specifically, the presence of the metal-containing asphaltenes results in catalyst deactivation by reason of the coking tendency of the asphaltenes, and the accumulation of metals on the catalyst.
Many proposals thus have been made for dealing with non-distillable fractions of crude oil and other heavy hydrocarbons, include residual oil which contain sulfur and other metals. And while many are technically viable, they appear to have achieved little or no commercialization due in large part to the high cost of the technology involved. Usually such cost takes the form of increased catalyst contamination by the metals and/or carbon deposition resulting from the attempted conversion of the asphaltene fractions.
One way that refineries have attempted to receive more value from heavy hydrocarbons including asphaltenes has been to gasify them. U.S. Pat. No. 4,938,862 to Visser et al. discloses a process for thermal cracking residual hydrocarbon oils involving feeding the oil and a synthetic gas to a thermal cracker, separating the cracked products into various streams including a cracked residue stream, separating the cracked residue stream into an asphaltene-rich stream and an asphaltene-poor stream, then gasifying the asphaltene rich stream to produce syngas which is fed to the thermal cracker.
Likewise, U.S. Pat. No. 6,241,874 to Wallace et al. discloses extracting asphaltenes through with a solvent and gasifying the asphaltenes in the presence of oxygen. Heat from the gasification of the asphaltenes is used to help recover some of the solvent used in extracting the asphaltenes.
Further, U.S. Pat. No. 5,958,365 to Liu discloses processing heavy crude oil by distilling the same, solvent deasphalting the oil, and further processing the heavy hydrocarbons to produce hydrogen. The hydrogen is used to treat the deasphalted oil fraction and distillate hydrocarbon fractions obtained from the heavy crude oil.
However, there still remains a need for a cost-effective and commercially viable method of extracting more value out of asphaltenes produced in refineries.